Ion beam sources with tiltable firing angle

ABSTRACT

An ion source for an electromagnetic separator is tiltably mounted upon the ion beam passageway. Adjustment of the inclination to the passageway of the ion beam trajectory is thus provided.

U nlted States Patent 1151 3,705,320

Freeman 7 1 Dec. 5, 1972 [$4] ION BEAM SOURCES WITH TILTABLE [56]References Cited FIRING ANGLE UNITED STATES PATENTS [72] Inventor: JamesHarry Freeman, Abmgdon,

England 2,585,702 2/1952 Thompson et al. ..313/14s x 2,506,660 5/1950Blattmann et ai. ..3l3/l48 X [7 Asslgneel The United Kingdom Atomic gy2,626,359 1/1953 Weber, Jr. um/149 x Authority, ondon, England 2,959,70011/1960 Campanile ..313/14s x 3,096,435 7/1963 Burdg ..313/63 X [22]1970 3,182,190 5/1965 Lilly, Jr. 8! al ..250/41.9 s13 [2!] Appl. No.:3,958

Primary Examiner-Roy Lake Assistant Examiner-Palmer C. Demeo [30]Foreign pplicamn Pnomy Data Attorney-Larson, Taylor & Hinds Feb. 5, I969Great Britain ..6,289/69 [57] ABSTRACT [52] 250/419 1 4 2 An ion sourcefor an electromagnetic separator is v tiltably mounted upon the ion beampassageway. Ad- IIEL Cl. justment of the inclination to the p g y of the[58] Field of Search 513/63, 230, 146, 148, 149, ion beam trajectory isthus provided 4 Claims, 6 Drawing Figures PATENTEDBEL' 51912 SHEET 1 [IF2 PATENTEDnac 5 I972 SHEET 2 OF 2 ION BEAM SOURCES WITH TILTABLE FIRINGI ANGLE 1 BACKGROUND OF-TI-IE INVENTION The invention relates toion beamsources, for example for separators.

In ion beam separators a beam containing ions of a plurality of isotopesis caused to pass through a strong magnetic field which extendssubstantially perpendicularly to the ion beam path. The magnetic fielddeflects the ions into a curved path, the magnitude of the deflectionbeing dependent, inter alia, upon the mass of the ions. Thus ions ofdifferent isotopes may be separated into diverging beams and byappropriate geometrical arrangement of the components of the separator,ions of a selected isotope may be focussed upon a chosen target.

SUMMARY OF THE INVENTION The invention provides an ion beam sourcecomprising a vacuum tight enclosure, means for generating ions in theenclosure, means for ejecting the ions from the enclosure in arectangular section beam from an extraction slit, attachment means forattaching the enclosurein vacuum tight communication with an enclosedbeam passageway, whichattachment means permits limited movement of theenclosure relative to the passageway for adjusting the relativeinclination of the ejected ion beam to the passageway, and constrainingmeans for constraining the enclosure, in its said limited movement, tofollow a pivotal motion about either of two perpendicular intersectingaxes, one of which is parallel with the said extraction slit andcoincident with the origin or apparent origin of the ion beam.

' Preferably the enclosure is attached to a beam passageway via a vacuumbellows. Conveniently, spherically machined relatively slidable surfacesprovide the said constraint upon the adjusting movement of theenclosure. Alternatively, the enclosure may be mounted on gimbals forpermitting the required limited movement. I I

BRIEFDESCRIPTION on THE DRAWINGS A specific construction of ionbeamsource embodying the invention will now be described by way of exampleand with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic perspective view of an electromagneticseparator to which the ion beam source is connected,

FIG. 2 is a diagrammatic plan view of the electromagnetic separator,

FIG. 3 is a diagrammatic representation of the ion source forillustrating the manner in which it is mounted on to the electromagneticseparator,

I Specification No.

DESCRIPTION OF PREFERRED EMBODIMENT pole pieces 21 disposed on each sideof the passageway The provision, indicated at reference 22, foradjustirig the position of the electromagnet 19 relative to thepassageway 13 and the provision of adjustable pole tips in the polepieces 21 is described in the abovementioned Patent Specification No.6288/69.

The ion beam source 11 comprises an outer cylindrical walled vessel 23and an inner cylindrical walled vessel 24. The arc chamber 25 andassociated components for generating. the ion beam are supported on andwithin the inner vessel 24. The outer vessel 23 is secured with a vacuumtight seal to theion beam passageway 13. 7

As may best be seen from FIG. 3, the inner vessel 24 is attached to theouter vessel 23 by a vacuum bellows 26. This arrangement permits somemovement of the whole ion source relative to the ion beam passageway 13so that adjustment of the inclination of the ejected beam to thepassageway 13 may be effected.

When making this adjustment, it is important that there is no lateralmovement of the extraction slit 27. This is achieved by the provision ofa spherically machined surface on the outer vessel 23, which surface isindicated at 28 and 29 in FIG. 3, and a co-operating sphericallymachined surface, indicated at 31 and 32, on a rim protruding from theinner vessel 24.

The centers of curvature of the spherically curved surfaces are arrangedto coincide with the extraction slit 27 so that, when the inner vessel24 is moved, the

surface 31, 32 slides over the surface 28, 29 and constrains themovement to be pivotal about a notional pivot at the center ofcurvature. As may be seen from the arrows denoted X in FIG. 1, thepivotal motion is permitted about two perpendicular axes, one of whichis parallel with the extraction slit 27 and is arranged to be coincidentwith the origin or apparent origin of the ion beam. An alternativemechanism for providing the required constraint upon the movement of theenclosure comprises gimbals, illustrated diagrammatically at 44 in FIG.6.

The components of the ion source which are housed within the innervessel 24 are shown in greater detail in FIGS. 4 and 5. FIG. 4illustrates the essential components for describing the principle ofoperation and FIG. 5 illustrates the structural layout of thecomponents.

As may best be seen from FIG. 4, the ion source operates upon theprinciple described in British Patent Specification No. 916703. Thematerial which it is desired to ionize is introduced into the arcchamber 25 as a gas. For this purpose it may be necessary to heat thestarting material and, for this, an oven 33 is provided behind the arcchamber 25. A filament 34 extends behind and along the length of theextraction slit 27. In operation, the filament is electrically heatedand held at a negative potential relative to the walls of the arcchamber. The filament 34 emits electrons thermionically and the gas inthe arc chamber is ionized by these electrons as they move, under theinfluence of the self-magnetic field generated by the current throughthe filament and a separately applied magnetic field in the directionindicated by arrow A (FIG. 4) from the filament 34 to the walls of thearc chamber. The ion beam is drawn out of the extraction slit by anextraction electrode (not shown).

The magnetic field indicated by the arrow A is produced by anelectromagnet indicated at 35 in FIG. 1.

The principal purpose of this magnetic field is to increase the distancetravelled by the electrons in the spiralling path which they follow fromthe filament 34 towards the arc chamber walls.

The ion source of this example has the property of so shaping theemergent ion beam that the beam appears to diverge from a virtual sourceof width significantly less than that of the actual extraction slit.This provides a corresponding improvement in the resolution of theseparator.

In addition to the components shown in FIG. 4, FIG. also shows heatshields 36 surrounding the arc chamber, a corona shield 37 surroundingthe whole ion source, the various electrical input leads 38, 39, 40, 41with their insulation 42 and a pipeline 43 for introducing a gaseousmaterial direct into the arc chamber 25.

The invention is not restricted to the details of the foregoingexamples.

I claim:

1. An ion beam source comprising a vacuum tight enclosure, means forgenerating ions in the enclosure, means for ejecting the ions from theenclosure in a rectangular section beam from an extraction slit,attachment means for attaching the enclosure in vacuum tightcommunication with an enclosed beam passageway so as to permit limitedmovement of the enclosure relative to the passageway and thereby providefor adjustment of the relative inclination of the ejected ion beam tothe passageway, and constraining means for constraining the enclosure,in its said limited movement, to follow a pivotal motion about either oftwo perpendicular intersecting axes, one of which is parallel with thesaid extraction slit and coincident with the origin or apparent originof the ion beam.

2. An ion beam source as claimed in claim 1, wherein the enclosure isattached to the beam passageway through a vacuum bellows.

3. An ion beam source as claimed in claim 1, wherein the saidconstraining means comprise spherically machined relatively slidablesurfaces.

4. An ion beam source as claimed in claim 1, wherein the saidconstraining means comprise gimbals upon which the enclosure is mounted.

1. An ion beam source comprising a vacuum tight enclosure, means forgenerating ions in the enclosure, means for ejecting the ions from theenclosure in a rectangular section beam from an extraction slit,attachment means for attaching the enclosure in vacuum tightcommunication with an enclosed beam passageway so as to permit limitedmovement of the enclosure relative to the passageway and thereby providefor adjustment of the relative inclination of the ejected ion beam tothe passageway, and constraining means for constraining the enclosure,in its said limited movement, to follow a pivotal motion about either oftwo perpendicular intersecting axes, one of which is parallel with thesaid extraction slit and coincident with the origin or apparent originof the ion beam.
 2. An ion beam source as claimed in claim 1, whereinthe enclosure is attached to the beam passageway through a vacuumbellows.
 3. An ion beam source as claimed in claim 1, wherein the saidconstraining means comprise spherically machined relatively slidablesurfaces.
 4. An ion beam source as claimed in claim 1, wherein the saidconstraining means comprise gimbals upon which the enclosure is mounted.